Although fixation of tissues using glutaraldehyde and formaldehyde have been a mainstay of numerous processes and procedures (i.e. histologic processing, etc.) related to medical practice in the past and present, inducing tissue cross-linking in the patient [Therapeutic Tissue Cross-linking (TXL)], for treating human disease, is novel. The rapid growth throughout the world of CXL (riboflavin photochemistry) in treating keratoconus (KC) and post-LASIK keratectasias (LASIK=Laser-Assisted in situ Keratomileusis) is proving that in vivo tissue cross-linking is possible and can be beneficial from a patient care standpoint. As good as it is, CXL has limitations, especially the need for debridement of the corneal epithelium (painful, infection risk, delayed healing, haze) and the use of ultraviolet (UV) light (with potential damage to the lens and retina, and even cancer risk). Our long-term goal is to develop therapies for human diseases through the use of in vivo therapeutic tissue cross-linking and to understand how enzymatic cross-linking contributes to the development of disease, specifically in KC. The overall objective of this particular application is to develop a nw treatment for corneal thinning diseases that will serve as a springboard for the development of similar treatments in other diseases (such as sclera in myopia, etc.). Formaldehyde releasing agents (FARs) are a promising group of chemical compounds, used widespread by the cosmetics industry as chemical preservatives in personal care products (PCPs). These FARs can be used for an alternative purpose, namely as therapeutic tissue cross-linking agents. The following aims will be pursued: 1. Using an ex vivo corneal cross-linking simulation set up that evaluates both cell toxicity and tissue fixation, establish optimal conditions for therapeutic corneal tissue cross-linking using FARs. 2. To test the hypothesis that topically applied FARs can induce corneal cross-linking in a safe and effective manner in the living eye. 3. To utilize analytical chemical methods (LC/MS and MALDI-TOF) to quantitate enzymatic collagen cross-links in keratoconus corneas and identify biomarkers of the induced cross-linking reactions (CXL and FARs). It is anticipated that these aims will yield: 1) A safe and effective method for inducing tissue cross- linking as a therapy for KC that leaves the epithelium intact and does not require use of UV light. 2) A deeper understanding of the role of enzymatic cross-linking in the pathogenesis of keratoconus as well as the development of new biomarkers for the therapeutic cross-linking reactions. Having the ability to cross-link the cornea using a topical cross-linking agent will open the door to applying this method to the treatment of other diseases in which mechanical tissue failure plays a role, including the sclera in progressive myopia.